Magnetic compass



' W. awr-MTE MAGNETIC COMPASS Filed MarchV 11, 1947 Sept. 30, l947.

6 Sheets sheet 1 i INVENTOR.

Sept. 30, 1947. w, G, W|||TE 2,428,346

MAGNETIC COMPAS S Filed March 11, 1947 l e sheets-sheet 2 Sept. 30,1947. w. s. WHITE MAGNETIC COMPASS `6` Sheets-Sheet 5 Fileld March l1,1947 a Foes HFT 2 f. 9 2. 70. 9 a @a Z 2 ya. UL W .vl 'I F a h ma 4 1 .w2

INVENTOR. M MT' vSQPLIO, 1947- f w. G. WHITEy 2,428,346

MAGNETIC COMPASS Filed March 11, 1947 6 Sheets-Sheet 4 IN VEN TOR.

SpLSO, 1947.v wge. WHITE 2,428,345

MAGNETIC coMrAss v Filed Maron 11, 1947 l @Sheets-shew 5 INVENTOR.

I "afgana 1mb Sept. 3o, 1947. w. G. WHITE MAGNETIC coMPAss Filed Marchl1, 1947 6 Sheets-Shea# 6 JNVENTOIL BY #a man I Patented Sept. 30,n 1947UNITED STATES 'PATENT OFFICE My invention relates to magnetic compassesand more particularly to an improved spherical' compass providinggreater accuracy and convenience than previous instruments known in theart.

There are two important compass problems toward the solution of which myinvention isaddressed. One in which the card will remain substantiallyin a given plane, unaffected by the rolling and pitching of the vesseland the resultant ,violent accelerations and shocks; this ideal cannot,however, be accomplished at the risk of decreasing the sensitivity o-fthe card to magnetic influences. The other principal problem is toovercome the error arising from the departure of the lubber line fromits perpendicular relation to the compass card, an error magnied in thecase of a sailing vessel sailing at a substantial angle of heel andsimultaneously pitching. In a spherical compass the card remainsfairlylevel, but the lubber line is inclined in varying amounts by the forcesacting on the pendulous bowl, andthe indicated heading may vary as much.as ten degrees as the ship rises and falls with` the seas. With a flatcompass the swirl of the liquid in the compass bowl inevitably inducesrotational moment to the compass card so that on relatively small ships,such as submarine chasers, thehelmsman must develop an inituitive senseconcerning the compass and automatically and unconsciously compensatefor such errors from moment to moment. The chief value of a conventionalspherical problem is to produce a compassV 12 Claims. (Cl. 33-223)compass is the stability resultingfrom the damping effect on the compasscard of the liquid lling the bowl. However, practical reasons makevitun` desirable to make the compass card large enough in diameter to takeadvantage of the maximum damping action available. To do so wouldinvolve employing heavier directive elements and supports, thusincreasing the mass of the card elements and defeating the dampingeffect by the increase in the ratio between the masses of the card andthe liquid. Furthermore the second problem would no-t be touched by theexpedient of increasing the diameter of the card.

I have invented a form of spherical compass which offers a solutioncommon to both problems. In one aspect my invention comprises asaucershaped member almost as large in diameter as theA inside of thesphere and mounted for cardanic movement substantially parallel to andadjacent the compass card in position substantially to bisect the sphereand lubber line.

providing a mount for the The damping effect of the nearly 55 equalvolumes of liquid above and below the member and the sympathetic dampingresulting from the juxtaposition of the card and the memberresult in acompass abnormally resistant to acceleration and shocks; when the shiprolls, the card and the member both remain level, and the angle betweenthe lubber line and the card remains constant.

more stable and accurate than instruments heretofore available.

Inasmuch as the liquid in the bowl is not set in motion when the compassis rolled, twisted, or otherwise moved, but remains quiescent, theliquid offers resistance to motion of the compass card and the saucer ordisk. This action is enhanced the more nearly the card and disk come tobisecting the sphere of liquid so that there are substantially equalvolumes of the liquid on both sides of the assembly. v I have found itis practical and beneficial to have the rim of the saucershaped member,the compass card, and the pivot point for the compass card all lying ina plane coincident with the equator of the bowl. This disposition of theelements results in optimum stability of the compass card and disk,deriving from the stability of the liquid. Furthermore, it is highlydesirable to construct the compass card f and saucer-shaped memberassembly from materials as light as is practical. The more nearly themass of the compass and saucer-shapedmember approaches a ratio of unitywith respect to the massl of liquid, volume for volume, the moreperfectly will the liquid serve to damp the compass card. It should bepointed out that the combination of the glass hemisphere and thecontained liquid forms a lens which magnies the indicia appearing on thesurface of the compass card. Consequently the card may be both small andlight, and the saucer-shaped member may be of greater area, thuspromoting stability.

In addition to the stated advantages obtained by the use of my novelcompass is the further feature that a compass so constructed may besecured rigidly to the ships structure without the costly and elaboratetrunnions and gimbal rings heretofore found necessary. Of course, if thecompass is to be associated with the conventional azimuth circle, itwill generally be found necessary to mount the compass in externalgimbals so that the azimuth circle will remain substantially level. f

While compasses constructed according to my invention are accuratenavigation instruments suitable Vfor use on ships and aircraft, thegreat Trials of compasses constructed according to my invention revealthem toY be much for purposes of illustration and shown in the'accompanying drawings, in which:

Fig. 1 is a view in cross section through the center of a compassconstructed in accordance with my invention,

Fig. 2 is a view in end elevation showing the response of the compass toa roll or heel,

Fig. 3 is a plan view of the compass with the cover removed,

Fig. 4 is an exploded elevation of the card mount assembly,

Fig. 5vis a bottom plan View of the magnet holder,

Fig. 6 is a View; partly in cross-section and partly in elevation, ofYanother embodiment of my invention,

Fig. 7 is an exploded elevation of the internal assembly of the compassshown in Fig. 6,

Fig. 8 is a ViewV in cross-section of a third embodiment of myinvention, and

Fig. 9 is a View in cross-section throughk a fourth type ofinternalcompass assembly.

,In the modification yshown in Figs. 1 5 the compass is mounted on acup-shaped base lll of brass, aluminum or other non-magnetic material;in order to provide for bottom` lighting there Vis provided a centrallydisposed hole l2 in the bottom of the base I0, it being understood thatthe compass may be mounted in a binnacle or other support having anelectric lamp arranged'beneath the base.4 I8; Secured to the base by anumber of brass screws i8 is a hemispherical shell or bowl i4 providedwith an-annular shoulder It dimensioned to fit snugly into the base l.The bowl. I4 may conveniently be of spun brass or other suitablematerial, although aI machined.

casting may beused'if desired.. The requirements are that the bowl be ofnon-magnetic material and thatthe inner wallY be. as close to a truehemisphere as is practically possible. Departure from the hemisphericalform, or the occurrence of iats, protuberances, etc., impairsr theability of the bowl to roll about the liquid filling it andy thus causesswirling and turbulent agitation 'of the liquid.

The bottom of the bowl vlli contains al opening 29 to the lower edge ofwhich is sealed an expansible bellows 22 defining an expansion chamber24 which changes in volume as the liquid expands or contracts inresponse to changes in temperature. A circular socket or frame 25 issealed to the bottom of the bellows 2li and carries a disk 280i glass orother translucent material heldin place by a gland 32 working against aflexible gasket 30. The hole i12, the disk 18, and the opening 20 arealigned to transmit light tothe interior voi" the bowl M. A pair ofdrain plugs are threaded into the wall of the bowl I4 approximately 180apart.

'fhe upper edge ofthe bowl I4 supports an integral outwardly projectingflange 38; also the upperedgereceivesthe lower edge of a stouty glasscircular hemispherefil? ground'` and polished to form as I nearly" vasVpossible .an optically correct true flange 38, is bevelled on its innerface, and works against a compressible gasket 44. A series of machinescrews d8 serves to hold the ring in place and clamp the glasshemisphere l2 to the bowl i4 in a huid-tight seal.

A pair of pivot pins 50 work in grooves formed in the upper edge of thebowl i4 at 180 intervals, arranged to lie in the fore and aft axis ofthe compass and in the equator thereof. The pivot pins 50 support alarge diameter, carefully balancedaluminum gimbal ring 52' normallysitting almost exactly in the equator of the compass and carrying asecond pair of pivot pins 54 (Figs. 2 and 3) arranged in the athwartshipaxis of the compass. (By fore and aft axis and athwartship axis I intendto imply the corresponding axes of the craft `in which the compass ismounted.) The pivot pins 5d work in bearings 55 mounted on the underside of a member 58 substantially concentric with the sphere of thecompass and made ofV thin gauge aluminum, magnesium, or very lighttranslucent plastic. The member 58 partakes generally of the appearanceof a shallow saucer; as shown in the drawings it includes a flat annularrim, broad enough to oifer substantial damping area, merging into anoffset flat center portion. By the term saucer-shaped member, I intendto designate any comparable shallow disk having a diameter suiiicientlylarge to cover asubstantially complete equatorial plane of thecontaining sphere. It will be found advisable to depart from a circularflat disk only to such an extent as maybe required to accommodate thecompass card and its pivot mount. The essence of. the invention lies inproviding a member suitably dimensioned to take full advantage of thestability of the liquid in the sphere, and the optimumv is the largestpractical amountV of surface lying in an equatorial plane and acted uponby approximately equal volumes of liquid. The gimbal ring 52 and thermember 58 are so dimensioned that the diameter of the latter is onlyslightlyless than' the inside diameter of the compass sphere, and thefact that the member is aproximately concentric with the sphere issignificant because the member may be tilted through 360' withoutstriking the inside wallv of the sphere. Two uprightv pins 60 are se'-cured to the disk 58 at' 90 intervals to serve as fore and aft lubberlines.

Secured tothe center of the member 53 by a pair! of clamping nuts (illvis a vertical: metal post 62 having a depending portion threaded toreceive a .balancing weightl and vprojecting upwardly as a hollowlpillar receiving the stem of a jewelled pi ot' cup 68` cooperating witha cone point pivot pin 'l0 mounted` in a shallow metal housing supportedon a conventionally marked,

flat compass card 'I4 made of thin, translucentV plastic materiali Thecompass card 'M lies within theldished portion of the member 58 and isaproximately in the same plane as the elevated margin thereof` The pointof the pivot pin Til, the compass card, and the margin of the member alllie normally in the equator of the bowl.

A bracket or frame 'I6 is provided with depending stirrups for holding apair of bar magnets 'i8 and is secured by a pair of screws 8l) to thehousing 12. Also a pair of bolts 82 secure the bracket directly tothecard. Y

SurroundingA the housing 1-2 and sealed to the compassl card lll isametalv cap 84 in turn housed in a larger-cap 86 also sealed tightly tothe card T4". The capsl 84- andldeiine between theml a fluid-tight floatchamber 88 to provide buoyancy counteracting the weight of the elementsand free the pivot for rotational movement. The pendulous Weight '66 isrequired to compensate for the dip of the magnets.

In selecting the materials to comprise the compass it is, of course,necessary to avoid the use of magnetic materials and also to employelements as light as is practical. Furthermore the best results will beobtained if the moments of the disk 58 and the compass card assembly arethe same, because they will then remain substantially parallel when thecompass is subjected to acceleration and movement. The weight 66 isadjusted until the member 58 is counterbalanced so that it will barelyovercome the friction of the pivots and seek a horizontal position.Also, the best results are obtained when the distance between the planeof the pivots 50 and the working surface of the jewel pivot 68 isminimum.

The entire compass is lled with a neutral liquid from which all gas hasbeen removed, the expansion chamber 24 takingv care of changes in thevolume of the liquid occasioned by variations in temperature.

The compass as a whole will of course move with the vessel on which itis mounted, but the liquid will remain undisturbed except for minor skinfriction of the inside walls of the container and the eddy currentsabout the supporting elements. Inasmuch as the liquid remainsundisturbed, there is no hydraulic force at work on the member,Which-may be regarded functionally as an inertia plane. The same is trueof the compass card. Consequently the card and the lubber lines retaintheir positions as before the vessel moved. When the vessel, whileupright, responds to a force introducing lateral accelerations at thecompass, the member 58 and the card 'I4 are subject to the sameacceleration since they have been adjusted to have the same verticalperiods. The members would respond to the acceleration were it not forthe fact that the member 58 effectively bisects the sphere of liquid.rThe ratio between the speciiic gravity of the liquid and that of thecompass card-and member 56, or inertia plane assembly is as close tounity as can practically be obtained. Consequently their response toacceleration is very similar and the development of diiferentialvelocities is minimized.

A second embodiment of my invention is illustrated in Figs. 6 and 7. Asbefore, the compass is mounted in a cup-shaped base |00 and includes e,bottom hemisphere |02 of spun brass or other suitable material providedwith a pair of drain plugs |04 disposed 180 from each other. Theexpansion chamber and associated elements are not shown, and it is to beunderstood that an arrangement similar to that shown in Fig. 1 isemployed. The bottom hemisphere is shouldered to receive the lower edgeof a true glass hemisphere |06 held in position by a retaining ring |68bearing on a circular gasket ||0 and clamped by screws to an outwardlyprojecting flange I |2 formed along the top side of the hemisphere |02.From points adjacent the bottom of the brass hemisphere |02 extend thelegs ||4 of a tripod support including a collar ||6 supported `by thelegs ||4 and permanently secured to a hollow sleeve ||8. Fitting intothe sleeve ||8 is a cylindrical post |20 adapted to be secured inadjusted position by means of a set screw |22 and serving as a mount fora vertically disposed stem |24 carrying a cylindrical head |26transversely bored to receive a pivot pin carried In turn, the gimbalring |28 is bored to receive.

a pair of'pivot pins |30 disposed in a line parallel to the thwartshipsaxis of the vessel and working in a small lug |32 having the shape of aninverted U. The lug is thus cardanically mounted for movement withrespect to the head |26. The lug, however, is not permitted to rotateabout the axis of the head |26 of the post |20. The lug |32 has a pairof outwardly extending feet |34 provided with tapped holes to receive apair of screws |36 which rst pass through an inverted light metal disk|38 and through 4'a large diameter flat, saucer-shaped member |40 whichis substantially the same as the member 58 described in conjunction withFig. 1, secured to the bottom of the disk |38 is an annular weight |42and it will be seen that the weight |42, the small inverted disk |38,the large member |40 and the lug |32 are clamped together as an integralassembly by means of th'e screws |36. As before, the weight |42 servesto maintain the member |40 level and may be regarded as a pendulum.

Mounted in the top of the lug |32 and in alignment with the stem |24 andthe post |20 is a stem |44 carrying at its upper end a jeweled pivotbearing |46. The stem |44 threads into the top of the lug |32 and ismaintained in position by means of a lock nut |48. The pivot bearing |46is retained in an internally flanged bushing |50 in the manner of a balland Socket joint so that th'e lug |32 and the pivot bearing |46 are freeto move universally with respect to the bushing |50. The bushing |50' isalso externally ilanged at its base and its barrel is externallythreaded. Resting on the base flange of the bushing |50 is a light metalcap |52 having an outwardly extending base ange |54 to the top of whichis soldered a pair of bar magnets |56. A Small disk |58 rests on the topof the cap |52 and provides a mount for an annular compass card |60provided with conventional indicia. An internally threaded cap |62carries in its top wall a cone point pivot |64 and engages the externalthreads on the bushing |50. The dimensions are such that the cap |62 maybe screwed onto the bushing |50 to clamp the disk |58 and the cap |52between the bottom of th'e cap |62 and the base ange of the bushing |50.Also the cone point |64 is engaged on the pivot bearing |46 and thewhole upper assembly is free to rotate universally from the pivotbearing.

It will be observed that the construction shown in Figs. 6k and 7 makespossible the elimination of the relatively large and heavy gimbal rringshown in Fig. 1. This in turn makes it possible to extend th'e diameterof the saucer-shaped member |40 nearly to the inner wall of the compassbowl. In principle the behavior of the compasses shown in Figs. 1 and 6is the same. That is to say, the member |40 is cardanically mounted. Itsexterior rim is in the same plane as the pivot point and the compasscard and is broad enough to present substantial damping area. As before,lubber lines |66 are secured to the member |40. The entire assembly maybe adjusted vertically by manipulating the set screw |22 and th'e post|20. The distance between the pivot point |64 and the pivot pinsl |30should be as short as possible since it is desirable to have bothcenters of pivotal movement lie as close as possible to the center ofthe sphere.'y As before,

it is bes't to @construct .all .of the elements'fof :the assembly vfromthe 'lightest materials :consistent withl requirements Afor strength andrigidity .since the `desired damping eiectzis :best :obtained 'when the:ratio of thespecific gravity nf the:liquidi-.and the compass assemblyapproaches unity. Also the :center of rotation .and-'the planes of theclompass .card :and the member :Hill should fas Vnearly as Lpossiblebisectthe sphereof .liquiddn thezcompassxbowl.

.As Ibeiorenoted the action or the compasses shown-in Figs. .l andvisiundamentallysthexsame. Theoretically :the embodiment .shown :in Fig. i6will be moreieicient :because `the gimbal ring has beenzreduced in size,but'the embodiment .shown in Fig. l offers certain manufacturing.advantagesfand can'besconstructed .more inexpensively. 'It should bepointed vout thatthe small volume between the'compass cardand thesaucer-'shaped member H15 is 4fully Acocupiedv by liquid and willproduce `a sympathetic Vaction lbetween vthe two if -either or `bothlare disturbed from :their settled positions. It Will be readilyapparent that the azimuthal swirl of the liquid Liollowing 'a violentdisplacement of the .compass element `from the magnetic meridian will bedamped .out rapidly by the .close .relationship of the card and themember 14). .It should .also be noted Ythat the 'free .action of lthecard in .the embodiment shown in Fig. ylis unlimited. Therefore 'thecompass need not .be mounted level but may be isecured Y`to an vinclinedsurface such as the dashboard .on an automobile. ,In the embodimentshownin Fig. 6 .the compass card may turn as much .as :85 `from theEhorizontal, a freedom of movement :more than suiiicient `for allordinary uses.

in 'Figrf -I have 'shown a :third embodiment -of my invention, basedonzthesame principles-that govern theabove described :modifications andoffering certain advantages. As .in the case of ,the compass V-shown 1inFig. 6, I .provide Vva cupshaped base |35 supporting a spun brasshemisphere 182 secured as before to 7a true glass hemisphere ldd. `Asbefore, ia sleeve `+86 .fi`ssup ported on a tripod support "i388 .andcarries `a v erticallyadjustablepost |96. A very smallgimbal ringi=92;is.pivotally supported .as showninFigsr and .7 vand Yabove'described and, as ibefore, a lug 119.4' is pivotally mounted iin the.gimbal ring. The lug [94 :is tapped ntofreceiverapair-of screws 1:95 fwhich pass 'through ;a `small .metal 'inverted dish 498 and a large.diameter .saucer-shaped member '220. The inverted .dish i238 fcarrieslan annular counterweight .252 and t'he :member '200 is provided Awithan outwardly lextending .peripheralfflange .20E towhich is securedasimilar-,flange 208 formed on .a transparent member ,210 similar to`the member '2&9 .but inverted. .A socket 2 l2 .depends from the centerofthelinvertedmember `2 l0 and is 'provided with `a threaded hole inalignment with 'the :post 19.0. stem 2M is threaded into the socket 2I2and locked in ad- I:usted :position by lmeans ;of -a nut 24B. On thebottom `.of the stem 2M .is an inverted jeweled pivot 'bearing 2I6retained iin an internally anged'bushingQ-ZD 'in the manner-.oi arba-lland a socket yjoint. kA cap 222 is :threaded `over the bushing-22|) andclamps to .it a small ring 224 to: which are secured internallyprojectingiianges oi' fa pair of Vvoppositely ydisposed annular vcasings226 which also "have outwardly :extending flanges embracing-and securedto :an annular -csmpass card 228.` Thercasings 226 -form"between themanairtight float chamber "2139.V -A tpair of 'bar magnets'232 aresoldered or otl'ierwiseY secured tothe bottom casing Y1226. .A pivotYpin 225 'is mountedin the bottom Wall ofthe cap 222. The buoyancy ofthe iioat, chamber .230 is suiiicient to float the compass cardassemblyand urgethe pivot point 225 into low pressure engagement with .thejeweled pivot bearing 218. It will be recognized that the pivot assemblyis almdstzpreciselysimilar'to that shown in Fig. 7 except that in Fig.'8 'it has been inverted. .A pair ofports 234 are ormedin the members200 and V2li) and provide means for the liquid to enter 4the chamber.defined between them. In this embodiment the compass card and assemblyof members 200 and 210 effectively bisect the sphere of liquid andthedistance between the top ofthe pivot pin 225 and the pivots for thegimbal ring |94 is .minimized. The construction shown in Fig. 8 offersthe further .advantage that the sympathetic damping action between themembers 2.00 and 2W and the compass lcard is greatly enhanced by reasonof the fact that the inertia plane, Viz. the members, extends on bothsides oithe .compass card. This construction relieves Athe supportingelements from the weight of l.the compass card so that all oi the pivotbearings will function almost indenitely. The principles .underlying theaction ofthe compass shownin Fig. 8 are the same as those operating inthe first two embodiments described and need not be repeated. It will berecognized that either of the members 260 and 2i l) could be replaced bya spider, without departing from the spirit rof the invention.

'In Fig. 9 I have shown, somewhat diagrammatically, a fourth embodimentoi the invention again employing a very small internal gimbal ring 25epivotally mounted on a head 252 carried on la vertically adjustable post(not shown) mounted on a tripod support, (also not shown). A ilug 254vis pivotally mounted on the gimbal ring i258 and provides support for adepending counterweight 256. Secured to the lug is .a bottomsaucer-shaped member or inertia plane'disk 25.8,.shaped as shown `inFig. 8, to which issecured a similar but inverted transparent mem- .ber:255. The members are ported as shown at 259 .and 261. The invertedmember 260 ncarries a centrally disposed socket .252 in which ismounteda jcweled pivot bearing 264 in alignment with the head `2:52 andalso aligned with a second jeweled pivot bearing 265 mounted on the topof the zlug .256. .A'double-ended pivot pin 2&8 'works in :the`-bearings 25d and 255 and carries a .bushing32 and a cooperatinglocking member 269 which clamps to the pin ESB-an annular compass card121i) `on which are mounted a pair of `flat barfmagnets 212. Lubberlines2M are'appropriately mounted on the bottom member 258.

In this 'embodiment vthe compass card 2-10 is mounted inthe Asame manneras the balance .wheel of va watch. It is 'free to rotate with respect totheot'hcr elements of the assembly about the axis .of the pivot pin 25S,but the plane of the compasscard will always remain parallelto'the'planes of the vmembers 258 and 2160. Accordingly `the angle.between the compass card and the lubber lines can never vary. Asbefore, the saucershaped Amembers function together as an inertia planebisectingthelsphere of liquid in the compass bowl .so that the maximumdamping action is obtained and .the yresult is a compass rmuch krmorestable tbanianythingfheretofore available. 4I vfeel it vunnecessary todiscuss further the theoryof the action :ci .the compass shownin Fig. 9`for the reason that itis similar to the discussions contained in thedescriptions of the preceding embodiments of my invention.

The essence of my invention lies in the provision of a shallow memberlying parallel to the compass card, substantially bisecting the sphereof liquid in the compass bowl, pivotally mounted with respect to thecompass bowl and with respect to the compass card, and providing supportfor the lubber lines. Such a compass is abnormally stable because theaforesaid member functions as an inertia plane picking up stability fromthe stability of the liquid in the bowl and by sympathetic dampingaction lending further stability to the compass card proper. In additionto the enormous increase in stability thus obtained, I simultaneouslystabilize the angle between the compass card and the lubber line. All ofthese factors contribute to make a much more eiicient and dependablenavigating instrument than has heretofore been known in the art. Thefact that I have illustrated and described four embodiments of myinvention does not mean that I have exhausted all of the possible modesin which my invention may be practiced, although they do represent themost practical and efficient embodiments of the invention now known tome.

Having now described my invention what I claim as new and desire tosecure by Letters Patent of the United States is:

1. A compass comprising a truly spherical con'- tainer having atransparent portion, a circular compass card disposed within saidcontainer and having substantially smaller diameter than the insidediameter of the container, a support for mounting said cardsubstantially concentric with said container, a saucer-shaped memberhaving a diameter nearly that of the inside of the container, a cardanicmount supporting said member closely adjacent and parallel to thecompass card, and a neutral transparent liquid filling the container,said member having substantially flat areas in contact with said liquid.

2. A compass according to claim 1 wherein at least one lubber line ismounted on the saucershaped member.

3. A mariners compass comprising a spherical bowl, a compass cardsupported for pivotal movement about a point substantially concentricwith the bowl, a saucer-shaped member disposed within the bowl, parallelto and adjacent the compass card in position substantially to completelybisect the bowl, a cardanic support for said member, a thin rod carriedon said member and projected beyond the edge of the card to form alubber line, and a liquid iilling the bowl, whereby i said member issubstantially damped by said liquid when the bowl is moved and in turndamps the compass card, and whereby the angle between the card and thelubber line is maintained substantially constant.

4. A magnetic compass comprising a spherical container, a gimbal ringpivotally secured to the inner wall of the container, a shallowsaucershaped member pivotally suspended from said gimbal ring and havinga diameter nearly that of the inside of the container, a compass cardpivotally secured to said member adjacent and par' allel thereto, and aneutral liquid lling said container, said ring, member, and card beingfree to move through 360 relative to the container.

5. A magnetic compass comprising a spherical container, a shallowcircular member including a flat rim and a slightly offset centerportion cardanically suspended within the container as a substantiallycomplete bisector of the sphere, a

10 compass card pivotally mounted within the container in positionnormally to lie adjacent and parallel to said member within said rim,and a liquid lling said container.

6. A magnetic compass comprising a spherical bowl, a support disposedwithin the bowl, a gimbal ring of small diameter pivotally mounted onsaid support, a saucer-shaped member pivotally mounted upon said gimbalring and having a diameter nearly that of the inside of the bowl, saidmember having a broad flat continuous rim and a iiat bottom offsetslightly from said rim, a pivot bearing mounted for movement with saidmember, a compass card smaller in diameter than said member, and a pivotcarried by said card and working in said bearing, the dimensions of theelements being such that the distance between the bearing and the gimbalring is relatively short, said card and rim being substantiallyco-planar with the normal horizontal equatorial plane of the bowl,

7. A magnetic compass comprising a spherical bowl, a pairofsubstantially flat dished members each being nearly as large indiameter as the inside of the bowl and secured together at their edgesin opposed relation to dene between them a chamber, a cardanic mountsuspending said members in said bowl, a pivot member secured to thecenter of each member and disposed within the chamber, a compass carddisposed between the members, and a pivot member secured to said cardand engaged with the pivot members on said dished members, and a liquidlling the bowl and said chamber.

8. A magnetic compass comprising a bottom hemisphere, a transparentupper hemisphere secured to the bottom hemisphere, a support secured tothe bottom hemisphere, a post mounted for vertical adjustment on saidsupport, a cardanic mount secured to said post, a circular member nearlyequal in diameter to that of the inside of the hemispheres and securedto said mount and having a Yflat annular portion wide enough to presentsubstantia1 damping area lying normally substantially in the plane ofthe equator between the hemispheres adjacent the peripheries thereof, alubber line mounted on said circular member, and a compass carduniversally pivotally mounted on said member, the pivot point for thecard being disposed substantially concentric with the hemispheres, whilethe aXes of the cardanic mount lie slightly vertically oiset from theplane of said equator.

9. A magnetic compass comprising a spherical bowl, a circular platedisposed in the bowl and having a iiat annular rim and a central portionoffset slightly from the rim and nearly parallel thereto, gimbalssupporting said platey said plate having a diameter nearly that of theinside diameter of the bowl, and a compass card smaller in diameter thanthe circular member and pivotally mounted thereon within the annularrim, the gimbals, the rim of the plate, and the compass card all lyingsubstantially in the same equatorial plane of the spherical bowl.

10. A magnetic compass' comprising a truly spherical bowl, a lightweightsaucer-shaped member cardanically mounted to lie normally in thehorizontal equatorial plane of the bowl and large enough nearly tocompletely bisect the bowl and a compass card universally pivoted uponsaid member and disposed closely adjacent and parallel thereto.

ll. A magnetic compass comprising a truly spherical bowl, a shallowsaucer-shaped member 'El nearly large', enough tot confer.Y @completeequatorial; planethroughxtrxe` bnwL, a: cardani'o mount arrangedi tsuspend said.: member'1 substantially in the normal horizontalequatorial plane of the bowl,` a. compass'. card smaller inarea: thanthat ofi the member; auniversal pivot mount carried by said; member' imposition to support,V the; com"- pass@ oardf closely' adjacent andparallel: to'v the member, and a liquid fillingtherbowl',there. beingsubstantially. equaal volumesfof liquid 4ori-either side of.-saidmember.

1-2.' A@ magnetic compass comprising a substantially-'sphericat bowl,@member having: a: at annular: rim; wide enouglr to: present substantialdamping,- areai andi a shallow.` bottom depressed below therim,` saidmemberhavingv an area vneen-li)v ll'ngran; equatorial plane of: thebowl; a. cardanio mount: arranged;V to; suspend said; member'with itsr'mr lying,l substantially irr the normal: horizontal equatorial; planeof the; bowl, ai pivot-"mount car'- ried by said member, a compass cardpivotally mounted om saidf` member; the rim; of thevr member, thiefVcard: and*` the; pivot point? beingv all substantially co-planar, andi aliquid' filling the bowl, said card .beingsubstantially'concentro'withthe -boWL WILFRID GORDON WHITE.

REFERENCES CITED rEhe following references are of record in the le ofthis patent:

UNITED STATES PATENTS.

Number' Name Date- 1,930,775k Sohweisthal Oct. 17', 1933 2,008,481 Weberet al July 16, 1935 2,026,919 Stright Jan, '1, 1936 2,300,685 McKay Nov;3, 1942 FOREIGN PATENTS Number Country Datev 54,503 Austria July 25',1912 507,889: Great Britain` June 22., 1939 705,549 Germany May 2, 1941762,684@ France Jan. 29, 1934

